The bones bore unmistakable signs of butchery: indentations where they were hammered open to expose the marrow within, cut marks left by knives used to tear the flesh away. They were scattered throughout the cave, and jumbled with the remains of horses and reindeer that had been similarly cut and bruised. When the scientists pieced the skeletons together, they formed five humans: four adults and a child.

The remains, which belonged to Neanderthals living in what is now Belgium between 40,500 and 45,500 years ago, are "unambiguous evidence" of Neanderthal cannibalism, scientists said this week in the journal Scientific Reports. They're not the first such find — other bones suggesting that the prehistoric hominins ate their own kind have been uncovered in France, Portugal and Spain. But the Belgian site is farther north than anything else that's been discovered, and it dates to a time toward the very end of the Neanderthals' existence, in the few thousand years before their species went extinct.

The researchers aren't sure why the bodies were butchered — was it part of a ceremony? An act of desperation? Sheer bloodlust? Instead, they say only that it "highlights the considerable diversity in mortuary behavior among the region's late Neanderthal population in the period immediately preceding their disappearance."

For decades, paleoanthropologists have pointed to funeral practices as evidence of Neanderthals' emotional sophistication. A burial is proof that the person was mourned, the logic goes, and if they were mourned that means they were loved.

But remains that have been buried for tens of thousands of years don't always mean what we think they do. Skeletons in Croatia that were identified as victims of cannibalism 100 years ago are now believed to have been marred by natural processes. In the 1970s, a paleoarchaeologist argued that a Neanderthal dubbed "Shanidar IV" had been laid to rest on a bed of flowers because crushed pollen was found under the bones.

"The Shanidar IV data have been used to support the notion that Neanderthals felt 'the love of beauty' and 'the full range of human feelings' characteristic of modern humans," anthropologist Jeffrey Sommer wrote in a 1999 review of the site. But more recent analysis has disputed that interpretation of the skeleton — it's more likely the flowers were left there by an animal, scientists say.

The researchers studying the Belgian bones are well aware of these pitfalls. "Neanderthal mortuary practices ... may provide insights concerning the social systems of this fossil human group," they write, but those behaviors "are difficult to interpret in Palaeolithic contexts."

So they stick to describing what they found: 96 bones and three teeth from five Neanderthal individuals, lying in a cave with other animal remains near the town of Goyet, Belgium. Pieced back together, the remains constituted five human bodies — four were teenagers or adults, the last was clearly a child. Nearly a third of the bones bore cut marks where they'd been hacked apart or the flesh had been torn away. Their rib cages showed signs of having been pried open.

The larger bones, femurs and tibias, were notched and pitted, suggesting that someone had tried to break them open to suck away the marrow. A few also bore marks of "retouching" — they'd been used to help sharpen stone tools. Whoever ate those people, it appears, later used their bodies as a whetstone.

Other animal bones, those of reindeer and wild horses, showed similar treatment.

Radiocarbon dating of the remains put them at roughly 40,500 to 45,500 years old. Modern Homo sapiens hadn't arrived in the region at this point, so the researchers conclude that the skeletons must have been butchered by their own kind.

Mitochondrial DNA analysis suggest that they were genetically similar to contemporary Neanderthal communities living in Germany, Spain and Croatia — suggesting that the Neanderthal population at the time was quite small.

That makes sense, because the Neanderthals were about to die out. The best estimates to date put their final extinction at 40,000 years ago — within a few thousand years, or perhaps even several hundred, of when the Goyet people were slain.

So, what does this mean? It's hard to say, the researchers acknowledge. There are four other Neanderthal sites within about 150 miles of Goyet, all dated to roughly the same time frame None of them show evidence of cannibalism. One site, a cave near the town of Spy just a few dozen miles away, contained two skeletons that appeared to have been buried together.

Perhaps this is evidence of behavioral variability: Neanderthals lived in small groups, so it's possible that some mourned their dead, while others ate them. Perhaps other circumstances — conflict, deprivation or something else — drove these Neanderthals to eat their own kind.

It's worth noting that practicing cannibalism might make these Neanderthals more like humans, not less. Fossils found at the Klasies River Caves in South Africa suggest that Homo sapiens ate their own kind as early as 120,000 years ago. There are still incidents of cannibalism today.